Fluidic heat sensitive device and system



United States Patent 3,417,813 12/1968 Perry 3,426,782 2/1969 Thorburn ABSTRACT: A heat sensitive fluidic device is provided having a cooling fluid jet stream passing thru a chamber which has a wall ofa predetermined length arranged adjacent to and divergent with respect to the direction of flow of the stream. The jet stream is arranged so as to attach to the wall by boundary layer lock-on. The wall is made ofa good heat conductor so that evaporation takes place in the boundary layer of the jet stream as sufficient heat is transferred thereto from the heat conducting wall. A vapor bubble or bubbles form in the boundary layer and cause detachment of the jet stream from the wall when the vapor bubble growth is sufficient to cause the boundary layer to pass the downstream end ofthe wall. The jet stream is automatically reattached to the wall after a short delay; this cycle ofjet stream movement is repeated if the wall remains above the predetermined temperature. The device not only provides cooling of the heat conducting wall within predetermined limits but also provides for detecting when a predetermined temperature has been exceeded.

3,530, 71 Patented Sept. 29, 1970 8 Sheet 1 of 2 FIG. 3

INVENTOR BERNARD J. GREENBLOTT ATTORNEY Patented Sept. 29, 1970 Sheet 2 of2 FIG. 4

RESERVE HEAD K OF COOLANT LOGIC MEMORY M T R c0 PU E X 34 I Y Y ELEC COOLANT POV /ER/ /j SINK R &MXORY 46 46 54 49 M This invention relates to a fluidic heat sensitive device, and more particularly, to a device capable of providing cooling within predetermined temperature limits and capable of detecting when a predetermined temperature has been reached.

In present day electrical component packaging arrangements, hot spots often develop. These may be particular components or areas which tend to overheat in comparison with the rest of the arrangement. Rather than designing the overall cooling of the arrangement or system to be sufficiently efficient to handle these hot spots or components, it is usually more economical to provide additional local cooling for the hot spots or components. The present invention provides a fluidic device capable of providing such additional cooling or capable of detecting a hot spot and signalling for additional cooling in the overheated area.

Accordingly, it is an object of the present invention to provide a heat sensitive fluidic device for providing local cooling within predetermined temperature limits.

It is another object of the present invention to provide a fluidic device for detecting when a predetermined temperature limit has been reached.

It is a further object of the present invention to provide a cooling system in which a fluidic heat sensitive device is utilized to detect a rise in temperature of a portion of a system beyond a predetermined temperature and signal for additional cooling of that portion of the system.

Fluid logic devices have been devised capable ofperforming the same logic functions as the well known electronic devices. The most important feature of these fluid logic devices is their extreme reliability in that no moving parts are involved. The basic operating concept is the switching of a fluid jet stream between different paths in response to various stimuli such as fluid impulses, electric impulses, etc. However, it has never been realized that these fluidic logic devices can be designed to provide cooling within built-in limits and to detect a temperature rise beyond a specified limit.

Briefly, the fluidic heat sensitive device includes a nozzle or orifice capable of producing a jet stream of cooling fluid. A chamber is provided through which thejet stream passes. The chamber has a wall of good heat conducting properties which has a predetermined length and is located adjacent to and divergent with the undiverted direction of jet stream flow. Heat generating components to be cooled are located in good heat conducting association with the wall. Means are provided. for diverting the jet stream toward the wall so that attachment by boundary layer lock-on takes place. The cooling fluid in the jet stream provides cooling of the wall when attached thereto. The jet stream enters a channel beyond the wall when the stream is attached to the wall. The jet stream automatically detaches from the wall at a predetermined wall temperature and reattaches to the wall automatically after a predetermined short delay.

A plurality of these fluidic heat sensitive devices may be utilized in a computer cooling system to detect overheating in any portion thereof. The computing system is a proportionally cooled system wherein a small fluidic computer keeps track of and directs the cooling fluid to the portions of the computer. The device detects that a predetermined temperature has been passed and signals the computer for additional cooling. If the full cooling capacity of the system is being utilized, the computer will gate in auxiliary cooling means from a standby unit.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

FIG. I is a schematic cross-sectional diagram of a fluidic device showing the jet stream attached to the heated wall.

FIG. 2 is a further cross-sectional diagram of the fluidic device showing the jet stream detached from the heated wall.

FIG. 3 is a cross-sectional diagram of the fluidic device showing a feed back channel which causes reattachment of the fluid jet to the heated wall.

FIG. 4 is a schematic representation of a computer system in which the heat sensitive devices of this invention may be utilized.

The fluidic heat sensitive device of the present invention consists of a housing 10 providing a nozzle 12 through which a fluid jet or stream is supplied from an inlet 14. The stream passes through a chamber 16 having a good heat conducting wall 18 adjacent to and arranged divergent with the undiverted direction of flow of the stream. The stream in its straight flow path encounters wall 20 which is arranged at substantially right angles to the flow. The wall 20 sets up turbulence in the stream which causes the stream to move away from wall 22 toward wall 18. The jet stream will attach to wall 18 because of boundary layer lock-on. As can be seen from FlG. I, the wall 18 is located at an acute angle with or diverges from the direction of flow of the stream so that the jet stream when attached to the wall 18 is diverted from its straight-ahead path. The divergence is sufficient to cause the jet stream to flow into channel 24. Boundary layer lock-on or Coanda effect occurs when a stream of fluid is issued from an orifice adjacent an inclined or offset surface defining at least one side of an interaction region or chamber. As the stream passes through the chamber, it entrains fluid in this region on both sides of the stream. If only one side wall is employed or the stream is closer to one side wall than the other where two side walls are employed, the stream is more effective in removing the fluid from the region on the side of the stream adjacent the one side wall than from the region on the other side of the stream. In consequence, the pressure on the former side of the stream is reduced and a pressure gradient transversely of the jet is produced.

The pressure gradient deflects the stream closer to the aforesaid side wall 18 and the stream becomes even more effective in removing fluid from adjacent the side wall. The action is cumulative and the stream is finally deflected into contact with said side wall 18, locking onto the wall downstream of the orifice. The point at which lock-on occurs is known as the point of attachment" and its location depends upon the relation between the width of the power stream orifice l2 and of the interaction chamber 16 near the power stream orifice; the angle that the side wall 18 makes with respect to the center line of the power stream; the length of the side wall and the density, viscosity, compressibility and uniformity of the fluid. The region lying between the main stream and the side wall and between the point of attachment and the power nozzle orifice I2 is known as the boundary layer region, this region being at a pressure below ambient pressure of the system when the stream is attached and contains an entrainment or boundary layer bubble 26. The fluid which is to be used is preferably a liquid having good cooling properties. However, the fluid is not limited to this kind of liquid or for that matter to a liquid. it would appear that air or other gas would operate as well as long as it provides a sufficient cooling medium.

The arrangement is such that the heated wall 18 is the heat sink of particular components or is at least in contact with a medium such as a cooling fluid which has already absorbed heat from the elements which it is to cool. Accordingly, the wall 18 must be made of a good heat conductor to transfer the heat from the heat generating source to the jet stream of cooling fluid. As shown in FIG. 1, the wall 18 can be one of the surfaces of the components 19 to be cooled.

As the wall heats up, the heat transfer to the jet stream fluid in the boundary layer will increase such that evaporation of the fluid will take place and a vapor bubble or bubbles will form. The vapor bubble adds to the bubble 26 formed in the boundary layer during lock-on and continues to grow until the boundary layer reaches the downstream end of the wall 18 thereby causing the jet stream to detach from the wall 18. The jet stream upon being detached from the wall 18 will follow the straight ahead path as shown in FIG. 2. The upstream fluid in channel 24 returns to wall 18 and provides cooling until the jet stream returns. The obstruction 20 to the straight ahead path causes turbulence in the fluid sufflcient to cause the jet to return to the wall 18 where it is reattached. The vapor bubble 26 which formed and caused detachment of the jet stream from the wall 18 condenses in the cooler fluid when it is detached from the wall as shown in FlG. 2. It will be appreciated, that the jet stream will oscillate between its attached and detached flow paths giving a pulse output for each oscillation from the unblocked channel 24. It has been found that the oscillations are not necessarily of a fixed frequency since the turbulence set up because of the blocked path when the jet stream is detached does not always form in the same way. The oscillations will only continue as long as the heated wall 18 is above the predetermined termperature for detachment. This predetermined temperature is dependent on the length of the wall 18. Making the wall longer would require a larger vapor bubble to provide detachment and accordingly would provide more cooling. The reverse is also true for a shorter wall 18. Thus, it can be seen that the wall length is determinative of the temperature at which the device will oscillate. A control port 2] is provided by means of which the jet stream can be switched from its wall attached position, if desired, at any temperature. The control port 21 is similar to and functions the same as the control ports used in the well known fluidic amplifiers.

The frequency of oscillation of the device can be stabilized by including a feed back channel 28 rather than an obstruction 20 as is shown in FIG. 3. The jet stream, when in its detached flow path, enters the feedback channel 28 such that it impinges on itself causing reattachment of the flow stream to the heated wall 18. The length of the feedback loop 28 is determinative of the frequency of oscillation of the device. In other words, increasing the length of the feedback loop 28 determines the length of time that the jet stream is in the detached flow position. It will be appreciated, that the length of the feedback path 28 has a considerable effect on the temperature or cooling which is provided to the wall 18. If the feedback path 28 is short, the frequency of oscillation will be high and the jet stream will be attached to the wall more frequently thus providing greater cooling. If the feedback path is long, the temperature to which the heated wall 18 can rise is considerably increased. Thus. the length of the feedback path is determinative of the upper temperature limit.

It will be appreciated, that the fluidic heat sensitive device described above can be used as a temperature limiter for cooling hot spots encountered for example in arrays of heat generating devices. The temperature within the device can be preset to a desired high and low temperature level by adjusting the values of the wall length, the length ofthe feedback loop, and the flow characteristics of the fluid. For example, to change the range of a temperature limiter from 80- lt')C. to a range of 80l25C., the length of the feedback path 28 is increased. The length of the heated wall 18 and the fluid flow characteristics such as the Reynolds number remaining fixed. lt should be noted, that the cooling takes place both when the jet stream is attached to the hot wall 18 and when the up stream fluid in channel 24 returns to the hot wall 18 in the absence of the jet stream attachment. Increasing the length of the heated wall 18 has the effect of reducing the upper limit of the temperature range, The fluid flow characteristics can be adjusted to affect the lower limit of the temperature range.

The heat sensitive fluidic devices may also be utilized as a combined thermal sensor and cooling device in a system where cooling takes place on demand from a portion of or the total system. In this application, the jet stream is attached to the heated wall 18 until the wall temperature increases sufficiently so that the boundary layer expands to the point where the jet is detached from the wall. The detachment of the jet signals the cooling system to respond to the increased demand for cooling all wall projections in that portion of the system. The signalling can be done by the lack of a pressure pulse which would be the case when the jet stream is no longer conveyed in the channel 24 directly beyond the wall 18 which the jet stream enters when attached to the wall. The device will continue to oscillate from its attached to its detached jet stream flow path as long as the wall stays above the predetermined temperature and signals the cooling system that additional cooling requirements remain in demand. Once the wall is sufficiently cooled below the predetermined temperature, the device will perform its normal cooling function.

A schematic representation of such a system is shown in FIG. 4 wherein a reserve or head of coolant fluid 32 (stored energy) is shown. The fluidic heat sensitive devices 34 are located in various portions of the mechanization. For example, at least one device 34 is located in each of the subsections of the system, the logic section or sections 36, the power section or sections 38 and the memory section or sections 40, 42. The fluidic computer 44 has a computing section consisting of logic devices which compute the desired direction and quantity of fluid flow in response to changing demands for cooling, and fluid amplifiers 46 for directing the flow of coolant to desired parts of the system. The net result is a complete fluid system capable of thermal sensing, computing, controlling and moving coolant to required areas of the computer without resorting to energy conversion from electrical energy to mechanical energy, etc. Initially, the standby head of coolant 32 that is held in reserve is established by the pumping system 48. The pump 48 maintains the coolant sink 49 at a capacity sufficient to meet the cooling demands ofa discrete portion of the system that is less then lOO percent of the system. The standby reserve 32 is utilized to respond to above the normal demand of the total system. The temperature limit control devices 34 are located in predetermined hot spot areas in the sub system boxes or arrays. As the temperature limit control devices 34 are switched or go into oscillation due to a rise in heat flux, a signal is sent to the fluidic computer, 44. The fluidic computer 44 analyzes the current demand on the cooling system and signals the appropriate fluid amplifiers 46 to direct coolant to the desired portions ofthe subsystem. When the cooling capacity of the sink is exceeded, the fluidic computer 44 is aware of this condition and signals the standby head of coolant 32 to direct flow to the particular subsystem demanding additional cooling. lt will be appreciated that this is but one of the many applications for the fluidic heat sensitive device ofthe present invention.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without dcparting from the spirit and scope of the invention.

l claim:

1. A fluidic heat sensitive device comprising:

means for producing ajet stream of cooling fluid within said device;

a wall ofa predetermined length having good heat conducting properties located adjacent to and diverging from the undiverted direction ofjet stream flow;

heat generating components to be cooled located in good heat conducting association with said wall;

means for diverting the jet stream toward said wall so that attachment by boundary layer lock-on takes place, said cooling fluid in said jet stream providing cooling for said wall during attachment thereto;

a channel for conveying said stream beyond said wall whensaid stream is attached to said wall; and

means for automatically detaching said fluid jet stream from said wall when a predetermined wall temperature is reached, said means for diverting the jet stream toward said wall causing reattachment of said jet stream to said wall after a short delay.

2. A fluidic heat sensitive device according to claim 1, wherein said means for automatically detaching said fluid jet stream from said wall at a predetermined wall temperature comprises adding vapor bubbles caused by evaporation of the fluid in the boundary layer in response to heat transferred thereto from said wall to the boundary layer bubble, detachment of said jet stream taking place when said bubble grows sufflciently to cause the boundary layer to extend beyond the end of said wall.

3. A fluidic heat sensitive device according to claim 1, wherein said means for diverting said jet stream toward said wall comprises an obstruction substantially at right angles to the undiverted path of the jet stream against which said jet stream impinges setting up turbulence and causing said jet stream to divert toward said wall.

4. A fluidic heat sensitive device according to claim 1, wherein said heat generating components form part of said wall.

5. A fluidic heat sensitive device according to claim 1, wherein said means for diverting said jet stream toward said wall comprises a feedback channel for conveying said fluid jet stream when it is in its undiverted flow path, said feedback channel causing the jet stream to impinge on itself causing the jet stream to divert from its undiverted flow path so as to reattach to said wall, the length of time of detachment being dependent of the length of said feedback channel.

6. A fluidic heat sensitive device according to claim 5, wherein said means for automatically detaching and means for diverting said jet stream causing reattachment to said wall produces oscillation of said jet stream between the attached and detached conditions of said jet stream with respect to said wall when said wall temperature remains above said predetermined temperature, said frequency of oscillation being determined by the length of the wall and the length of the feedback channel.

7.A fluidic heat sensitive device according to claim 6. wherein said oscillation of said jet stream between the attached and detached conditions produces a pressure pulse and no pulse, respectively in said channel for conveying said stream beyond said wall.

8. A fluidic heat sensitive device comprising:

means for producing ajet stream of cooling fluid within said device in a predetermined direction;

a wall ofa predetermined length having good heat conducting properties located adjacent to and diverging from the predetermined direction of jet stream flow;

means for diverting the jet stream toward said wall so that attachment by boundary: layer lock-on takes place, said cooling fluid in said jet stream providing cooling for said wall during attachment thereto;

a channel for conveying said stream beyond said wall when said stream is attached to said wall; and

means for automatically detaching said fluid jet stream from said wall when a predetermined wall temperature is reached, said means for diverting the jet stream toward said wall causing reattachment of said jet stream to said wall after a short delay. 

